Implementing a Simple File Restore Mechanism

Imagine you're building a system that needs to save and restore the state of a crucial data file. This mechanism will allow users to save a "snapshot" of the file's content at a specific point in time and then restore the file to that saved state if needed. This is a fundamental concept in data management and version control.

Problem Description

Your task is to create a Python class, RestoreManager, that can save the current content of a specified file to a backup location and then restore the file from that backup.

Here's what needs to be achieved:

• Saving: The RestoreManager should be able to create a backup copy of a given file. This backup should be stored in a designated directory.
• Restoring: The RestoreManager should be able to replace the current content of the file with the content from its most recent backup.
• File Handling: The class should handle cases where the original file, the backup directory, or the backup file might not exist.

Key Requirements:

1. Initialization: The RestoreManager should be initialized with the path to the file to be managed (original_file_path) and the path to the directory where backups will be stored (backup_dir_path).
2. save() method:
   • Takes no arguments.
   • Creates the backup_dir_path if it doesn't exist.
   • Copies the original_file_path to a new file within backup_dir_path. The backup file should be named with a clear identifier, such as the original filename appended with a timestamp or a sequential number. For simplicity, let's use the original filename with a .bak extension. If a backup with this name already exists, it should be overwritten.
   • Should raise an informative error if the original_file_path does not exist.
3. restore() method:
   • Takes no arguments.
   • Checks if a backup file exists in the backup_dir_path corresponding to the original_file_path (e.g., original_file_name.bak).
   • If a backup exists, it should replace the original_file_path with the content of the backup file.
   • If no backup file is found, it should raise an informative error.
   • Should handle potential errors during file restoration (e.g., permissions).

Expected Behavior:

• The save operation creates a reliable copy.
• The restore operation reliably reverts the file to its saved state.
• The system gracefully handles missing files or directories.

Edge Cases to Consider:

• The original file does not exist when save() is called.
• The backup directory does not exist when save() is called.
• No backup exists when restore() is called.
• The original file is modified after a save, and then restore() is called.

Examples

Example 1: Successful Save and Restore

# Setup:
# Create a dummy file 'my_data.txt' with content "Initial data."
# Create a backup directory 'backups'

# Call save()
# The file 'backups/my_data.txt.bak' should be created with content "Initial data."

# Modify 'my_data.txt' to "Modified data."

# Call restore()
# The file 'my_data.txt' should now contain "Initial data."

Example 2: Restore When No Backup Exists

# Setup:
# Create a file 'config.ini' but do NOT call save()

# Call restore() on 'config.ini'
# Expected Output: An error like "No backup found for config.ini."

Example 3: Saving a Non-Existent File

# Setup:
# Assume 'important_log.txt' does not exist.

# Call save() on 'important_log.txt'
# Expected Output: An error like "Original file 'important_log.txt' not found."

Constraints

• The file paths provided will be valid strings representing file system paths.
• The implementation should use standard Python libraries (e.g., os, shutil, pathlib).
• The backup filename should be derived from the original filename by appending .bak.
• The backup_dir_path can be a relative or absolute path.
• Consider that file operations might fail due to permissions; handle these gracefully with informative error messages.

Notes

• When implementing the backup filename, ensure it's clear which original file it corresponds to, especially if you were to extend this to manage multiple files. For this challenge, appending .bak is sufficient.
• Think about how you will handle file copying. The shutil module in Python is very useful for this.
• Error handling is crucial. Use try-except blocks to catch potential FileNotFoundError, PermissionError, and other relevant exceptions.
• For the restore() method, you might consider overwriting the original file directly or writing to a temporary file first and then moving it for atomicity (though direct overwrite is acceptable for this challenge).